I was having issues with my Cadillac Catera 2001 3.0L V6 which is a version of the equivalent Omega.
I checked performance curves for Bosch for my alternator by duly reviewing the pulley ratios for crankshaft and alternator pulley. The standard Idle on my engine without Aircon on is 500RPM and with Aircon on it is 625RPM.
As can be seen with the attached chart the Alternator/Generator delivers virtually no amps and if you have idle at 500RPM and got your accessories and it is a hotter day you will see the voltage start dropping on extended idle or stop and go.
I installed a 1.7" pulley (nominal 1 3/4") versus the standard 2.21" (nominal 2 1/4") and the curve shows how it will help stabilize the electrical load versus generation. The chart Axis are Y-Axis Amps output of alternator and x-Axis is the Engine RPM. To not confuse I have converted x-axis to engine RPM whereas Bosch charts show the Alternator RPM.
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It clearly shows that for my Idle conditions will improve as follows,
Idle no-Aircon at 500RPM ---> From 0 Amp to almost 35 AMP+
Idle with Aircon at 625RPM --> From ~ 40 AMP to ~80 Amp
Any comments as I believe it may rob a little bit of power (haven't noticed any and car is very happy).
Hope it is of help or generates ideas.
PS: To compensate for smaller pulley I used a slighly shorter Auxiliary Drive Belt to ensure good tension with the auto tensioner and the following part number,
Gates Part Number: K060790
Interchange Part Number: 6PK2005